Preparation and spray application of a rapid thickening resin system



Oct. 20, 1970 RAFFEL ETAL 3,535,151

PREPARATION AND SPRAY APPLICATION OF A RAPID THICKENING RESIN SYSTEMFiled Aug. 2, 1967 FIBER Am CUTTER AIR-MOISTURE CUT FIIAMENTS 34 sq I20AIR\ AIR RESIN PRESSURF REGULATOR 24o WATER REGULATOR 2 INVENTORSBERNARD D. RAFFEL RAYMOND W. SHEA TSLEY ATTORNEYS United States Patent 03,535,151 PREPARATION AND SPRAY APPLICATION OF A RAPID THICKENING RESINSYSTEM Bernard D. Ratfel, Akron, and Raymond W. Sheatsley, North Canton,Ohio, assignors to Goodyear Aerospace Corporation, Akron, Ohio, acorporation of Delaware Filed Aug. 2, 1967, Ser. No. 657,977 Int. Cl.B0511 7/04 US. Cl. 117--105.5 4 Claims ABSTRACT OF THE DISCLOSURE Thisinvention relates to a method for providing a rapid thickening resinsystem whereby a dry resin sensitive to moisture is sprayed withmoisture selectively added to the resin during spraying whereby theamount of moisture added controls the thickening of the resin systemwhich is sprayed. The same technique is applicable for making prepregsby methods other than spraying.

I-Ieretofore, it has been well known to spray resin of the polyestertype from nozzles to provide a reinforced plastic system which may becured either by heat or at room temperature, and further where shortlengths of fiber glass strands are added to the sprayed mixture toincrease the final strength of the system. For example, US. Pat. No.3,073,534 shows a suitable nozzle for spraying resin, while Pat. No.3,118,336 shows a fiber cutter which can be used to deposit smalllengths of cut fiber into the sprayed resin from the nozzle. All priormethods of forming this type of resin system have carefully avoided anyuse of moisture as water has been harmful to the final properties of thesystem. However, when using a chemically thickened system, it has beenfound that the thickening time for a sprayed polyester resin and cutfiber reinforcement varies anywhere from one to several days or weeksbefore desired molding can take place due to the variation of moisture.At present all attempts to provide effective control towards thethickening or setup time of the system have been unsatisfactory.

In the molding of glass fiber reinforced polyester resins wherein thematerial flows to fill the die cavity, during the flow of material asthe dies are closed, it is important that the reisn and fibers flow insuch manner that:

(1) Resin does not separate from the fibers, resulting in resin-rich andglass-poor areas;

(2) The fibers do not become preferentially oriented with the directionof flow, resulting in anisotropic properties;

(3) The fibers do not buckle and bend as they flow to the edge of thepart, producing surface waviness.

It has been found that the desirable flow characteristics can beachieved by increasing the viscosity of the polyester resin to somethingaround or 20 million centipoises (at room temperature). At lowerviscosites, the undesirable phenomena mentioned above are encountered,although various techniques can be used to minimize their importance. Atthe higher viscosities, as the resin flows, it carries fibers along withit in generally random manner without preferential orientation andwithout separation. Also bending and buckling of fibers at the edge ofthe part are minimized, if not eliminated.

However, it is not feasible to impregnate fibers with resins ofviscosity much greater than, say, 8000 c.p.s. The solution is toimpregnate in a low viscosity stage, and then advance the viscosity. Todo this with polyesters has not been practical prior to the recentintroduction of the inorganic metallic thickening compounds such asmagnesium oxide and magnesium hydroxide.

Patented Oct. 20, 1970 Other advantages have accrued to thickening.These are:

(1) Greater ease of handling the molding stock because of non-tackycondition;

(2) Improvement in surface smoothness due to better fiber submergence,and the higher pressure molding accompanying the higher viscosity.

Therefore, the general object of the invention is to provide a processwhich can selectively control and effectively increase the thickeningtime of a sprayed polyester resin having short lengths of cut fibertherein. This control is achieved by using moisture sensitive thickeningagents to the resin before spraying, and then adding less than about 1%water to the system as it is sprayed.

For a better understanding of the invention, reference should be had tothe accompanying drawings in which:

FIG. 1 illustrates a typical spray system to achieve the method of theinvention; and

FIG. 2 is a schematic illustration of a typical system to provide adesired moisture content to the mixture when sprayed.

With reference to FIG. 1 of the drawings, the numeral 10 indicatesgenerally a resin spray nozzle which might be of the type illustrated inUS. Pat. No. 3,073,537, and which essentially utilizes an air line 12 asan input to provide pressure for spraying resin supplied thereto overline 14. In order to add fiber or cut filaments to the sprayed resinsystem, a fiber cutter 16 is provided to feed through a tube 18 into thenozzle 10. The sprayed resin builds up as a system 20 onto a receivingsurface 22, and can either be cured or formed to the surface upon whichit is sprayed, or built up to large proportions in sprayed layers andthen molded to a desired configuration. Other techniques besidesspraying might be used to form the resin system, also, and utilize themethod of the invention described hereinafter.

The objects of the invention, however, are achieved by utilizing a resinsystem which is substantially completely dry, that is with a minimumamount of moisture definitely less than 0.2% but sensitive to moisturefor the rate of reaction towards thickening. The invention particularlycontemplates the use of a polyester resin with an appropriate thickenersuch as MgO, Mg(OH) or Ca(OH) which are sensitive to moisture in thesystem for their rate of reaction. Moisture normally in the form ofwater or H O may be added to the nozzle 10 through a line 24, either inliquid form or at nearly saturated gaseous form so that in the sprayingprocess, the moisture is incorporated into the resin system 20 depositedon surface 22. The resin which is in the tanks, and passes throughsuitable plumbing to the line 14 can thus be kept dry, and so thickeningcan be controlled to almost any desired amount so that, for example, thesprayed resin system can be set to thicken so that it can be properlymolded in one day or less by adding a predetermined amount of water ormoisture saturated air.

Steam would be one method of adding air at nearly 100% moisturesaturation in line 24, although a direct water or moisture connection tonozzle 10 might be separately added. Also, it would be possible tosimply control the humidity in the air line 12 so that it would benearly at a relative humidity necessary to add the proper amount ofwater to the sprayed mixture.

A typical apparatus which might be utilized to selectively add moistureto the system is shown in FIG. 2. Specifically, a moisture regulator 30is provided and driven by an air pressure source over line 32. Theregulator 30 may be one made by Finn and Fram, Los Angeles, Calif, andis easily adjustable to inject as the last step any selected amount ofwater into the air delivered to air line 24a feeding into nozzle a.Normally the air will be provided from a suitable pressure source 34,and is controlled in pressure by regulator 36, dependent on the needs ofthe system.

A high degree of control on the percentage of moisture added is quiteimportant when spraying resins having critical demands so that a preciseamount of moisture is added in the last stage. In testing the apparatusand method of the invention it was found that on critical resins of thistype, if the moisture were added to the resin in the tanks beforespraying, that the resin would tend to start setting up in the tanks.And even so, with spraying begun immediately to avoid the setting up inthe tanks, under conditions of very low humidity the final sprayedcomposite would not set up at all because so much moisture had been lostduring the spraying. Thus, the need for practicing the method of theinvention is almost absolutely necessary when spraying resins criticalin their setup upon the amount of moisture present therein.

It has been found that the addition of between about 1% to of thethickening agent to the resin can then selectively control thickeningwith the addition of less than 1% water. In other words, the combinationdescribed will thicken the resin normally having a viscosity of betweenabout 2,000 to 10,000 centipoise to a viscosity of between about 2 to 30million centipoise within as short a time as about 1 to 5 hours, butpreferably so as to be properly thickened in Within 24 hours for propermolding characteristics.

Thus, it is seen that the objects of the invention are achieved bymaintaining of low viscosity mix or resin in the tanks to be sprayed toprovide a long working life thereof, yet selectively controlling thecuring or thickening rate of the resin system sprayed by incorporatingmoisture sensitive components in the resin, and selectively addingmoisture to the resin system as it is sprayed.

The magnesium oxide or hydroxide compounds used to cause thickeningrequire moisture to function and a rather precise amount for the properthickening rate. If less than about 0.1-0.2% of moisture, hardly anythickening occurs; if more than about .5 to .6% of moisture, thickeningcan occur in a fraction of an hour or even minutes so that there isinsufficient time to process through the equipment.

It has been found that the amount of water present in the resin systemis dependent upon atmospheric humidity. The resin system can gain orlose moisture depending upon the relation of moisture in the system tomoisture in the surrounding atmosphere. The amounts of water needed tobe added to the mix will vary with humidity and with Water introducedfrom other sources. For example, water is introduced:

(a) From absorbed moisture on fillers added to the resin, especiallyclays;

(b) Water is absorbed (or lost) during mixing of the resin with itsvarious compounding ingredients;

(0) Water is absorbed (or lost) from atomizing air and induction air inthe spray nozzle;

(d) Water is absorbed (or lost) as sprayed material is exposed toambient air; and

(e) Water may be present in the resin from absorption during storage, orresidual from the original manufacturing process.

(f) From moisture on the glass fibers.

To effect the correct amount of moisture in the final resin system afterspraying by addition of liquid water to the resin during mixing,requires that the amount of water' introduced from the sourcesabove-outlined be known,

The only way that has been found to control the total amount of finalmoisture under all conditions in the prodnot so that thickening occursin 24 hours or less after spraying, yet does not occur so rapidly thatthe sprayed material cannot be processed, is to add the moisture at thelast stage, which is spraying.

By this invention, one can provide for the addition of moisture at thespray head alone, and in sufiicient amounts to compensate for all lossesduring processing. As one method to pin-point the exact amount thatshould be added at the spray head, resin can be processed through thesystem, and after spraying, a sample collected and analyzed for watercontent by one of the rapid automatic moisture analyzers such as theBeckman Aquameter as made by Beckman Instruments Company. The waterinjector 30 can then be adjusted until the correct amount in the sprayedresin is obtained. Other suitable methods to determine the proper amountof moisture to be added may also be utilized.

While in accordance with the patent statutes, only one structure forachieving the method of the invention is illustrated and described; itis to be understood, however, that there might be many other structuresto achieve the method of the invention, and that the scope of the methodto be covered is set forth in the appended claims.

What is claimed is:

1. A method for providing a rapid thickening resin system which includesthe steps of spraying a substantially dry liquid polyester resin mixedwith a moisture sensitive thickener from a class including MgO, Mg(OH)and Ca(OH) onto a surface to form a system, while selectively addingmoisture to the mixed resin and thickener as it is sprayed whereby theamount of moisture added Will control the thickening of the resinsystem.

2. A method according to claim 1 where the moisture added is water andwhere it is added in the form of small water droplets interspersed withair in the spraying technique.

3. A method according to claim 1 Where the moisture added is water, andwhere it is added by utilizing air to achieve the spraying and whereinthe humidity level of the air used for spraying is controlled dependingon the amount of moisture necessary to be added to the resin.

4. A method according to claim 1 where reinforcing fibers areselectively added to the resin as it is sprayed.

References Cited UNITED STATES PATENTS 2,641,586 6/1953 Nordlander etal.

3,110,690 11/1963 Friedsam.

3,124,553 3/1964 Cordts 26037 X 3,240,736 3/1966 Beckwith 26037 X3,324,663 6/1967 McLean 26040 X 3,373,129 3/1968 Kori et al. 26040 X3,440,086 4/1969 Kerns 117-1055 3,049,439 8/1962 Colfman 239428 X3,050,262 8/1962 Curtis 239428 X 3,214,103 10/1965 Kempthorne 239428 XALFRED L. LEAVITT, Primary Examiner J. H. NEWSOME, Assistant ExaminerUS. Cl. X.R.

ll716l; 118-300, 600; 239428

